1. Field of the Invention
The present invention relates to a camera lens system, and more particularly, to a telephoto lens system for forming the image of an object on an image plane.
2. Description of the Related Art
Recently, digital cameras or video cameras including a solid-state imaging device such as a charge coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS) have been widely used. In particular, the demands for megapixel camera modules have increased, and compact digital cameras with more than 5 million pixels and high quality have been developed. There are still demands for smaller, lighter, and cheaper optical image forming apparatuses such as digital cameras or mobile phone cameras using a solid-state imaging device such as a CCD or a CMOS.
In video cameras or digital cameras, bright telephoto lenses having a low f-number (Fno) are preferred. However, such bright telephoto lenses are large and heavy, and auto-focus cameras with low f-number have a particularly slow focusing speed. To solve the problems, many attempts have been made. For example, a lens system has been disclosed that includes a front lens group and a rear lens group, and moves only the rear lens group. The rear lens group of this lens system acts as a focusing lens group consisting of 5 bright lenses each having an F-number of 1.4, to reduce the weight of the focusing lens group. However, since the 5 bright lenses constitute the focusing lens group, there is a limitation in reducing the weight of the focusing lens group. As another example, a lens system has been disclosed that performs inner focusing by using a focusing lens group including 5 bright lenses each having an F-number of 1.4 to reduce the weight of the focusing lens group. However, since the 5 bright lenses constitute the focusing lens group, there is also a limitation in reducing the weight of the focusing lens group.